1. Field of the Invention
This invention relates to metallic contacts to compound semiconductor devices, and, more particularly, to metallic contacts that are compatible with anodic formation of a native oxide used to passivate the semiconductor surface.
2. Description of the Prior Art
Compound semiconductor devices include devices which are fabricated employing mixed valence semiconductor materials; examples include II-VI compounds such as (Hg,Cd)Te, IV-VI compounds such as (Pb,Sn)Te, and III-V compounds such as GaAs, InAs, InSb, (In,Ga)Sb and In(As,Sb). Typical devices include photoconductors and photodiodes.
Such devices made in the past utilized either a non-oxidizing top contact metal such as gold or a rapidly diffusing metal such as indium. Following such metallization, a native oxide would be anodically grown to passivate exposed portions of the semiconductor surface. Use of the foregoing metallic contacts present many problems. For example, gold distorts or shorts out the electric field in the anodizing electrolyte, thereby causing non-uniform oxide thickness. Such non-uniform oxide thickness causes variation in the degree of accumulation or depletion of charge at the interface between the semiconductor and oxide, thus causing non-uniformity in the electrical characteristics of the device. The gold is also electrochemically attacked and often etched away during the anodization process, thereby yielding oversized devices and/or a rectifying junction at the interface between the active area of the device and the contact metal. On the other hand, it is known that indium will diffuse into and eventually destroy certain devices, such as those employing (Hg,Cd)Te.